The mobile phone industry has had an enormous development both regarding quality of service and transmission capabilities, as well as the technology for producing advanced communications terminals. In only a couple of decades the communication systems have gone from analogue to digital, and at the same time the dimensions of the communication terminals have gone from briefcase size to the pocket size phones of today. Still today, mobile phones are getting smaller and smaller and the size is generally considered to be an important factor for the end customer. The development in electronics has made it possible to miniaturize the components of the terminals, at the same time making the terminals capable of performing more advanced functions and services.
Mobile phones communicate by radio, and electromagnetic interference (EMI) will therefore always be an issue to handle. Electromagnetic fields generated from the radio part of the phone may cause interference problems ion the processor part, and vice versa. In order to shield sensitive equipment from electromagnetic radiation, or to protect them from electrostatic discharge, such equipment is often provided with a shielding device in the form of a metal casing or can, enclosing the equipment towards a carrier, typically a printed circuit board (PCB). In general, the can is soldered to the PCB to provide a conductive seam to a support surface on the PCB. An advantage with shield cans is that the cost of the can as such is low. However, a problem related to this method is that if a component below the soldered shield can is to be replaced or removed, the can first needs to be removed by heating and then be re-soldered after finishing the job with the component. This is a time-consuming and costly process.
An alternative solution is to apply a conductive gasket over a conductive trace on a PCB about the equipment to be shielded, and then apply a cover on top of the gasket. Such a conductive gasket may be provided as a string of silicone, in which silver grains are homogenously dispersed. A problem related to this technique is that such conductive gaskets generally are relatively hard. Moreover, they tend to become even harder by ageing. This means that the force needed to obtain sufficient contact between the cover and the conductive trace is quite high. Furthermore, in order to obtain a reasonable softness in the silicone, it cannot comprise a large amount of metal grains, which as such are non-compressible. As a result the contact resistance between the conductive silicone and an engaging surface is relatively low. Furthermore, the material cost for silver-containing silicone is relatively high.